In recent years, there has been a large amount of time and effort expended in the development of endoprosthetic joints of various kinds including such joints for replacement of various joints relating to the wrist and hand. This effort has manifested itself in a large volume of literature, both patent and otherwise, relating thereto. Much of this effort and resulting literature has, however, been directed toward joints relating to the wrist and fingers and a problem has continued to exist with respect to the thumb carpometacarpal joint. This is true in spite of the fact that said joint is an extremely common source of problems, such as arthritic problems, and is one of the most important joints of the entire hand for carrying out most manual manipulations. This problem appears to occur because of the relatively small bones in the hand adjacent the base of the thumb which have in the past appeared to preclude the successful anchoring of a prosthesis therein. For example, in U.S. Pat. No. 4,106,128, Greenwald et al, both the navicular and lunate bones of the hand, together with a portion of the capitate in the illustration shown with respect to the middle finger, are removed to provide room for the placement therein of the prosthesis with the base portion thereof being anchored in the radius bone. It is clear, however, from a mere inspection of the drawing in this patent that the middle finger is permitted to pivot at only one point and that this point is closely adjacent the radius bone rather than at the base of the finger itself. If this same treatment were applied to the thumb as suggested in said patent, the same problem exists, namely that the point of pivoting is too far from the base of the thumb to provide the desired natural motion.
Accordingly, the objects of the invention include:
1. To provide an endoprosthesis primarily intended for application to the thumb carpometacarpal joint which will closely simulate the movement of a natural joint.
2. To provide such a prosthesis which can be inserted between the trapezium and the first thumb metacarpal whereby the center of movement is at the natural position therefor adjacent the base of the thumb.
3. To provide a prosthesis, as aforesaid, which can be readily modified for use between the navicular and the first thumb metacarpal in those cases where the trapezium has disintegrated, with the center of movement of the joint still positioned at the natural point for same adjacent the base of the thumb.
4. To provide a prosthesis, as aforesaid, which will be simple to install by presently known techniques and may be so installed rapidly and efficiently.
5. To provide a prosthesis, as aforesaid, whose design embodies the maximum amount of presently known technology in order to secure long and successful operation thereof with a minimum of additional experimentation being required.
Other objects and purposes of the invention will be apparent to those acquainted with devices of this general type upon reading the following specification and inspection Zof the accompanying drawings.